<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="content-type" content="text/html;charset=UTF-8">
    <title>css2</title>
    <style type="text/css">
        span.highlight{
            background-color:yellow;
        }
        .hi{
            background-color:red;
        }
    </style>
</head>
<body>
<p>
  <span class="highlight">123</span>
    asdf.
    2ewq.
    sadfa.
    <span class="hi">1234</span>

</p>
<a class="highlight">sdfas</a>   <!--class 不生效-->
<p class="hi">sdfasf</p>
<a class="hi">3w4r243</a>
</body>
</html>